1. Field of the Invention
The present invention relates to turbomachinery blades, and more specifically to axial flow blades with untwisting capability.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
Axial flow turbomachinery blades, such as those used in a compressor, operate at high rotational speeds. The blades extend from a rotor toward a blade tip. In order to improve a flow performance of the turbomachine, the blades are designed with a certain amount of twist in the airfoil cross section. The amount of twist in the airfoil near the rotor is less than is the amount of twist in the airfoil near the tip. This is due to the higher circumferential rotational speed of the blade tip. Because the blades do not untwist during high rotation speeds, variable inlet guide vanes are used in a turbomachine like a gas turbine engine compressor to direct the air flow into the compressor blades.
As the turbomachine increases in rotational speed, the blade tends to untwist due to the imposition of centrifugal force on the blade. A blade is designed so that the blade will untwist at a certain rotational speed and at a certain amount (of untwist). The turbomachine is therefore designed to operate at a high efficiency only at that certain design speed. Rotors operating at a higher rotational speed will untwist further and result in lower performance. U.S. Pat. No. 4,334,824 issued to Tsuchikawa et al on Jun. 15, 1982 and entitled FLEXIBLE FAN DEVICE shows a flexible fan device in which the blades twist due to centrifugal force due to increase speed of rotation. The blades are solid and the fan is a relatively low speed fan used in an automobile engine. Because of this, the blades can be made from a thin material. This design would not work in a high speed turbomachine such as an axial flow compressor because the blades would have to be of such thickness (for structural rigidity) that untwisting would not be enough to increase the performance. U.S. Pat. No. 3,795,462 issued to Trumpler, Jr. on Mar. 5, 1974 and entitled VIBRATION DAMPENING FOR LONG TWISTED TURBINE BLADES shows a row of steam turbine blades with solid blades that can untwist due to high centrifugal forces. However, a steam turbine still operates at relatively low speeds compared to a turbomachine such as a compressor.
U.S. Pat. No. 6,669,447 B2 issued to Norris et al on Dec. 30, 2003 and entitled TURBOMACHINE BLADE discloses a gas turbine engine fan blade with a hollow interior of the airfoil portion being at least partially filled with a vibration damping material bonded to at least one internal surface. The damping material is a viscoelastic material. In the Norris et al patent, the blade is made of a metal material and thus would not provide the amount of untwisting as would the composite blade of the present invention. The hollow metal blade of Norris will untwist slightly more than a solid metal blade, but not enough to provide a high efficient blade as in the present invention.
U.S. Pat. No. 7,070,390 B2 issued to Powell on Jul. 4, 2006 and entitled COMPONENT WITH INTERNAL DAMPING discloses a turbine blade used in a gas turbine engine in which a hollow airfoil is formed by bonding a pressure side wall to a suction side wall with a thin internal panel disposed in a cavity formed between the two walls. The internal panel is secured in the root portion between the two walls and extends freely up into the cavity with the tip end free floating. The cavity is filled with a visco-elastic damping material. The blade of Powell will untwist from the centrifugal forces due to high speed rotation. However, the untwist will not be enough to increase the performance level of the blades in the high range of operating speeds in which the present invention is designed for.
It is therefore an object of the present invention to provide for a turbomachine with blades that untwist to its optimal aerodynamic level at different rotational speeds.
It is another object of the present invention to provide for a compressor in which inlet guide vanes are not needed.